1. Field
Example embodiments relate to semiconductor device and method of fabricating the same. Other example embodiments relate to a semiconductor device with a bipolar transistor and method of fabricating the same.
2. Description of Related Art
A semiconductor device has a variety of unit components (e.g., resistors, capacitors, metal-oxide-semiconductor (MOS) field effect transistors and/or bipolar transistors). Those bipolar transistors may be operable at an improved, increased frequency compared to the field effect transistors. The bipolar transistors may be more widely used in electronic devices requiring a higher-frequency operation. A conventional method for manufacturing such a bipolar transistor is as follows.
FIGS. 1 and 2 are sectional views showing a method of fabricating a conventional bipolar transistor. Referring to FIG. 1, a field isolation film 2 may be formed in a semiconductor substrate 1, defining active fields. The semiconductor substrate 1 may be doped with N-type impurities. The active fields may be correspondent with collector regions. P-type ionic impurities may be injected into the surface of the active field, forming a base layer. After depositing a first polysilicon film to contact the base layer 3 on the semiconductor substrate 1, the first polysilicon film may be patterned to form base electrode 4. The base electrode 4 may contact a top edge of the base layer 3. The top center of the base layer 3 may not be covered by the base electrode 4. The base electrode 4 and the base layer 3 may be doped with P-type impurities, conductively contacting the base layer 3. A first oxide film 5 may be deposited on the semiconductor substrate 5 and then patterned to form a hole 6 that partially exposes the base layer 3.
Referring to FIG. 2, after depositing a second polysilicon film (not shown) on the semiconductor substrate 1 to fill the hole 6, the second polysilicon film (not shown) may be patterned to form an emitter electrode 7. The emitter electrode 7 may fill the hole 6 and may contact the base layer 3. The emitter electrode 7 may be formed of polysilicon doped with N-type impurities. The emitter electrode 7 may complete an NPN bipolar transistor that is formed in a stacked structure of the collector region doped with N-type impurities, the base layer 3 doped with P-type impurities, and the emitter electrode 7 doped with N-type impurities. Before depositing the second polysilicon film, N-type ionic impurities may be injected into the top of the base layer 3 exposed by the hole 6, forming an emitter diffusion region.
A second oxide film 8 may be deposited to cover the emitter electrode 7 on the semiconductor substrate 1. The first and second oxide films 5 and 8 may be sequentially patterned to form an emitter contact hole 9a and an base contact hole 9b that expose the emitter electrode 7 and the base electrode 4, respectively. An emitter plug 10a may be formed to fill the emitter contact hole 9a and a base plug 10b may be formed to fill the base contact hole 9b. On the second oxide film 8, emitter and base interconnections 11a and 11b may be formed to contact the emitter and base plugs 10a and 10b. 
According to the method of fabricating such a bipolar transistor, while forming the hole 6, the surface of the base layer 3 exposed by the hole 6 may be damaged by a plasma etching operation. An interface characteristic between the emitter electrode 7 and the base layer 3 may deteriorate causing the bipolar transistor operational characteristics to worsen.
The top of the emitter electrode 7 may be higher than the top of the base electrode 4. In other words, a height from the bottom to the top of the emitter electrode 7 may be larger than a height from the bottom to the top in the base layer 4. Emitter resistance may increase rather than base resistance. As the emitter of the bipolar transistor further includes a portion (e.g., the emitter electrode 7) that has a higher resistivity than a metal, relative to the base, the emitter resistance of the bipolar transistor may become larger than the base resistance. The bipolar transistor may deteriorate.
The emitter electrode 7 may be partially formed on the first oxide film 5. Accordingly, the emitter contact hole 9a may only penetrate the second oxide film 8, while the base contact hole 9a penetrates the first and second oxide films 5 and 8. The emitter contact hole 9a may be shallower in depth than the base contact hole 9b. During an etching operation for a complete hole structure of the emitter contact hole 9a, the emitter electrode 7 exposed by the emitter contact hole 9a may be over-etched deteriorating contact resistance between the emitter plug 10a and the emitter electrode 7.